1. Field of the Invention
This invention relates to catalysts for the oxidation of sulfur dioxide. More particularly it relates to supports for such catalysts.
Sulfuric acid is produced on a commercial scale by the vanadium-catalyzed oxidation of sulfur dioxide to sulfur trioxide in the gaseous phase followed by absorption of the sulfur trioxide in an aqueous solution.
It is advantageous to disperse the vanadium active element on a microporous carrier or support. The support has a variety of beneficial functions including a high surface area to increase reaction rate, high porosity to maximize diffusion, physical integrity to minimize dusting, thermal resistance so that the vanadium composition may be molten without fusion of the catalyst particles, molded shaped form to minimize pressure drop, and chemical inertness. Until the instant invention a support providing a catalyst with both high activity and outstanding durability was unknown.
2. Description of the Prior Art
A wide variety of materials has been used as supports for the vanadium type of oxidation catalyst employed in the process for preparing sulfuric acid including brick dust, pumice, zeolite, fuller's earth, clay, quartz, diatomaceous earth, kieselguhr, and silica.
In reissued U.S. Pat. No. 18,380 filed in 1927, granted as U.S. Pat. No. 1,675,308 in 1928 and reissued Mar. 8, 1932 to Jaeger a non-siliceous series of base-exchanging materials are disclosed as catalysts for oxidizing sulfur dioxide including metallates of aluminum, chromium, zinc, vanadium, berryllium, tin, palladium, platinum, titanium, zirconium, tungsten, lead, uranium, tantalum, boron and molybdenum. These are incorporated with siliceous diluents or carrier bodies such as kieselguhrs of all kinds, diatomite brick refuse, pumice meal, pulverized quartz, sand, other minerals, and metal granules. Also disclosed are "celite", neutral silicates, silica gel, ground rocks, tuffs, lava, quartz filter stones, diatomaceous stones, aluminum granules, ferrosilicon, ferrovanadium, ferrochrome, aluminum polysilicates, ground glaucosil, infusorial earth, "celite" earth, "celite" brick refuse, colloidal silica, vanadyl silicate, and other acid-resistant siliceous minerals.
U.S. Pat. No. Re. 19,282 based on U.S. Pat. No. 1,371,004 filed by Slama and Wolf in 1914, granted in 1921, and reissued in 1934 discloses as supports for vanadium-type oxidation catalysts moist pumice powder, natural or triturated kieselguhr, precipitated silicic acid, stannic oxide and stannic hydroxide.
In U.S. Pat. No. 1,696,546 granted to Jaeger and Bertsch on Dec. 25, 1928 the following supports for the catalytic oxidation of sulfur dioxide are disclosed: zeolites and their pseudomorphs analogous to nepheline, leucite, feldspar and the like with exchangeable and non-exchangeable cations of a wide variety of metals; titanium dioxide; and, pulverized rocks rich in quartz, powdered glass, pumice meal, asbestos meal or fibers, kieselguhr, silica, pumice stones, diatomaceous stones, filter stones, quartz, acid-resistant minerals or rocks; roughened metals or metal alloys such as chromium, ferrochromium, ferrovanadium, ferromolybdenum, ferrosilicon manganese, ferrosiliconaluminummanganese, ferromanganese, ferrotitanium, ferrotungsten, ferronickel, ferrochromenickel; burnt pyrites, rutile, ilmenite, titaniferrous iron ore, "celite", manganese oxide, chromium oxide, bauxite, copper oxide, nickel oxide, cobalt oxide, iron oxide, barium oxide and the like.
U.S. Pat. No. 1,862,825 granted to Laury June 14, 1932 discloses powdered diatomaceous earth or "celite" brick chips, both fired to a temperature of about 1000.degree. C. to fuse the particles into a massive form, as supports for vanadium oxidation catalysts.
Krempff discloses in U.S. Pat. No. 3,216,953 granted Nov. 9, 1965 the use of finely divided porous silica as a support for a vanadium-type oxidation catalyst. One such is levilite. Also disclosed is a mixture of 90% natural kieselguhr and 10% carbon black. Silica gel may also be employed, as may micronized siliceous material. In addition to carbon black, micronized sulfur may be used to increase the porosity by burning during calcination of the catalyst mixture.
U.S. Pat. No. 2,029,376 granted to Joseph on Feb. 4, 1936 teaches the use of kieselguhr, finely ground pumice, precipitated silica, stannic hydroxide, or stannic oxide as supports for a vanadium-type catalyst expanded by the combustion of a polysaccharide gum.
The Johns-Manville Co. of Denver, Colo. published a brochure in March 1977 entitled "Glossary of Celite Mineral Filler Applications". On page 17 of this brochure there appears the notation that unspecified "Celite" diatomite fillers may support the vanadium catalyst used in the manufacture of sulfuric acid. At least 36 grades of diatomaceous "Celites" are describe in this brochure.
3. Objects of the Invention
An object of the present invention is to provide a support which can be utilized to form durable, useful, vanadium catalysts in the "contact" process for the oxidation of sulfur dioxide. Another object of the invention is to provide a support for the metallic catalysts of the "contact" oxidation process which furnishes catalysts with a high level of catalytic activity. Other objects of the invention will be apparent to those skilled in the art from the description and examples below.